What separation do you try to apply between your IFR traffic and unknown VFRs in Class E? In the UK there's no requirement for separation, only provision of traffic information. Then again there's very little Class E left in the UK and a substantial chunk of it was re-classified as Class D a couple of years ago as a result of an airprox between a 737 and a microlight.
In an ideal world airlines operating passenger flights into airports in Class E airspace ought to be required to carry out a risk assessment. Very few airline pilots know the implications of the difference between Class E and other categories of controlled airspace.
NS